It has long been known that the sewer pipe network which, since the 19th century, has consisted preferably of concrete pipes, is in need of reconstruction. This is in particular true for conurbations and large cities. In the Federal Republic of Germany alone it is estimated that several million meters of sewer pipes are in need of reconstruction. Alongside with the exchange of sewer pipes, recourse is often had, for sewer pipe reconstruction to a technique termed "relining method". In this connection a distinction is made between a so-called long pipe relining and a short pipe relining. With this method, plastic pipes are pushed or pulled in existing pipes which have ceased to be water-tight and which are usually made of concrete, stoneware, cast iron or the like. The hollow space left between the plastic pipe and the sewer pipe is filled in with an injection compound for the purpose of stabilization and sealing of the overall pipe network.
In long pipe relining use is made almost exclusively of high pressure polyethylene full-walled pipes and polypropylene full-walled pipes which, at the site concerned, are welded flush to the thrust surfaces as required by production or transport. In this connection it is known from U.S. Pat. No. 4,754,781 to use a flexible composite pipe, the inner pipe of which and the outer pipe of which must be made respectively of very soft flexible plastics to make possible a pulling of the plastic pipe into an existing sewer pipe, the pipe having to be flexible around a very narrow radius of curvature. This extreme flexibility of the pipe, for a simultaneous adequately high crushing strength, is not achievable as the claims of flexibility and rigidity are not mutually combinable. In addition, this system is not functionally viable as, after the introduction of the injection compound and the pulling around an extremely close radius of curvature the pipe made in soft plastic will collapse at least partly.
From European published patent application 0 275 055 it is known, with respect ot a plastic full-walled pipe, to provide at one end a protruding socket end and at the other end to form a top narrowed down in diameter. Pipes joined together are assembled externally flush or level with the bottom and thus exhibit on the outer surface none of the projections which increase the diameter of the pipe. Such full-walled pipes are used for the so-called short pipe relining, by means of which the drawbacks of long pipe relining, on the one hand, and disturbing earthwork, on the other hand, are considerably avoided. A substantial drawback of these full-walled pipes lies in that, to achieve an adequate crushing strength, they have to be very heavy, and thus with a very great wall strength and in that, on pulling or pushing in the pipes, leakages are produced in the plastic pipe as a result of breaks in the sewer pipe to be lined. Independently of resistance considerations this pipe must have a certain minimum wall thickness, because, from said thickness, the spigot at one end and the socket end at the other have to be formed, it being necessary in some cases to accommodate axial connections also between the two. In addition, such a pipe is only cumbersome to produce, as socket end and spigot either have to be made subsequently by machining, or socket end and spigot have to be formed on subsequently by injection moulding.
A long pipe relining is known from German published patent application 1,955,488, in which a pipe is first reamed and then provided with a pipe-like lining of polyethylene, with mortar being injected into the gap between the inner surface of the pipe and the outer surface of the plastic pipe introduced.